The present invention relates to a new and improved apparatus for monitoring the weft thread in a weaving machine or the like.
In its more specific aspects the invention relates to a new and improved apparatus for monitoring the weft thread in a weaving machine, especially in a pneumatically operated weaving machine, which includes a sensing or scanning head comprising a transmitter and a receiver and sensing the weft thread. The monitoring apparatus further includes a signal processing and evaluating circuit connected to the sensing head.
An apparatus of this kind as known, for example, from German Patent Publication No. 2,513,356 comprises a transmitter section including at least one source of radiation and a receiving section including an even number of radiation detectors. The radiation sources and the radiation detectors are arranged at the internal circumference of a ring through which passes an insertion medium. Each radiation detector receives the radiation emanating from only one radiation source. The transmitter and the receiver are connected to a differential amplifier and a processing and evaluating device for the signals which are formed by the differential amplifier during a monitoring time interval, and such transmitter and receiver are also connected to switching means for cutting off the weaving machine. A comparator circuit in the processing and evaluating device is periodically placed into an operationally preparatory state by a switching device for predetermined monitoring intervals. The comparator circuit compares the signals with a reference or set value.
In another state-of-the-art apparatus as known, for example, from German Patent Publication No. 2,105,559, a ring-shaped weft-thread conveying fork is provided at each end thereof with a photoelectric transmitter and receiver which furnish a signal when the weft thread passes therethrough after the same has been inserted and beaten-up at the existent woven material, and which also furnish signals in the event that the weft thread is absent.
A known weft-thread monitoring device in a pneumatic weaving machine including a transport channel formed integrally with the reed comprises a transmitter and a receiver at the end of the reed on the catch side thereof. In case of different weaving widths different reeds of varying and corresponding widths have to be employed in order that there can be used the weft-thread monitoring apparatus.
In a further known weft-thread monitor there is required in the signal processing and evaluating means or circuit a sensitivity adjustment which has to be manually performed a number of times per day, depending upon the degree of contamination or soiling, so that the weft thread may be detected by a sensing beam of rays extending between an oscillator-supplied transmitter and a receiver. A selective amplifier, a rectifier, and a smoothing member are series connected to each other and to the receiver; to the smoothing member there is connected a comparator for comparison of the signal with a reference voltage supplied by a potentiometer, and a light-emitting diode is connected such as to indicate a weft thread which has been detected by the sensing beam of rays. In such an arrangement the weaving machine and the adjustment thereof must be continuously manually monitored.